Sister
by ArtemisApollo97
Summary: Potentially a series of one-shots where Percy finds out that Louisa, my OC, is his long-lost twin sister (that he didn't know about). Each one-shot will be different, 'cos I can't settle on the one idea for Percy finding out he has a twin :) T for possible swearing
1. Chapter 1

**Originally for one of the Percy-finds-out-he-has-a-twin-sister fics, but I'm posting it as a one-shot 'cos I've recently been in the mode to write one-shots of Percy finding out he has a sister in several different ways.**

* * *

"Travis, take half of your cabin and go left. Connor, can you do the same, but go right?" The Stoll brothers nodded eagerly, setting about to get their cabin separated. Annabeth looked at her half-brother, Malcolm. "Can you organize our cabin?" He nodded. "Thanks." Annabeth smiled gratefully. Before addressing the next cabin, Annabeth scanned the demigods' faces, searching for Percy, despite knowing that if he were here, he would be at her side and not awaiting orders.

Annabeth pulled herself together. She had five minutes to quickly organise the last set of twelve cabins that were participating. Now that there were so many cabins and demigods, only twelve cabins could play at once, split into two teams.

But today, they were up against the Hunters of Artemis. Annabeth had been ecstatic to see Thalia again, but her mood had been dampened at the few previous games. Even if they went into one game and quickly into another, the Hunters energy was quickly restored. The campers hadn't won. Yet.

Annabeth was determined for the twelve Olympian cabins to win. She hadn't played against the Hunters before. The others had and had told her how difficult it was, but Annabeth's determination only grew stronger.

"Can anyone see Percy?" The match was about to begin, but Percy hadn't returned with the new camper, Louisa, who had wandered off. Chiron had insisted on her participation in the capture-the-flag match.

"He's on his way!" Leo replied, sitting on a low branch of a nearby tree.

"Thanks Leo. Ah… could you get down?"

"Why?"

"I'm not sure the nymph is too happy with a flammable boy in her branches."

"Uh…oh, ok." Leo jumped down. The nymph materialized briefly and kicked Leo in the shin, with a smug smirk on her face. A few laughed as Leo hopped about, massaging his new injury. He muttered something and a pinecone hit him in the side of the head.

"Leo, chill." Piper appeared, in her armour. Leo was glaring at the tree. Piper sighed and hooked her arm through his. "You really need to sleep more, Leo." Piper dragged him away from the tree.

Annabeth felt a hand on her shoulder. Turning her head, she saw Percy smiling at her as he tried to catch his breath. Behind him stood Louisa, who was looking at the other demigods, who were all wearing their armour. Annabeth noticed Louisa's lack of protection gear.

"Percy, you OK?" He nodded, grinning.

"She's… hard to find…" He breathed.

"Which explains why you're out of breath." He nodded in agreement. "Where's her armour?" Percy looked Louisa up and down before scowling. "Oh, Seaweed Brain! How could you forget?! The Hunters will kill her!" Percy smiled sheepishly.

"I'm missin' somethin'. What's goin' on?" A few of the Ares kids snickered. Louisa sent an evil glare in their general direction.

Leo's half-sister, Nyssa, took pity on her and explained the rules of capture-the-flag. Louisa understood. "Has anyone got any spare armour?"

"I got a helmet!" Travis replied. He passed it forward. Louisa took it, giving the plume an approving look.

"I take it you like red?" Percy asked her.

"It's an awesome colour." Louisa said, balancing the helmet on her fist.

"You're going to need that." Annabeth told her.

"Not really." Louisa said simply. "Thick skull, small brain." Louisa explained, rapping her knuckles on her head. Percy, Annabeth and most of the others snickered.

Louisa grinned at them before securing the helmet. Body armour was passed forward from someone in the Demeter cabin, who wasn't feeling too well.

Louisa was armed with her watch, but they didn't know that.

"Want a shield? Sword? Something?" Annabeth asked.

"No, I'm good thanks." The conch horn sounded and the cabins split up. "What am I doin'?"

"Whatever you want." Annabeth replied, remembering Chiron's orders. They still hadn't determined Louisa's godly parent.

"Cool." And she was gone.

* * *

Louisa was running through the forest, without an aim. Her instincts picked up on an approaching enemy before her hearing did.

She had just concealed herself in a tree when two Hunters burst into a clearing. One was Thalia- Annabeth's friend from earlier. The other was of similar height to Thalia, with thick auburn hair and sky blue eyes. Both were armed with silver bows and arrows, yet Thalia had a sword in her belt.

Louisa debated picking a fight with these two, but a shout caught her attention. She looked right as five children of Ares, including Clarisse, charged the two Hunters from the opposite side of the clearing.

Thalia drew her sword and met them head on, her weapon clashing with Clarisse's. Thalia's friend skirted the edges of the clearing, firing arrow after arrow. Louisa almost gagged on the strong stench of fart arrows. Too many caused a horrible smell that Hunters weren't fazed by.

Louisa recognized the next arrow as the Hunter stopped beneath her. A net arrow that, if fired correctly, could trap the demigods and leave them struggling for hours at a time.

Louisa whistled and the Hunter looked up, the arrow still ready to fire. Louisa dropped down as the Hunter darted away, aiming the net arrow at this new opponent.

"Where'd she come from?" Thalia shouted, ducking a slash from Clarisse's half-sister.

"She was in the trees!"

"Shoot her down, Karla!" Karla took aim and shot. Louisa summoned her sword and slashed at the arrow, sending the two silver halves tumbling to the ground. Karla stared at her, wide-eyed with awe and what Louisa hoped to be a bit of fear.

Louisa grinned wickedly.

"Thalia!" Thalia slammed her shield into Clarisse before risking a peek. Seeing Louisa free and armed, Thalia threw her shield (like Captain America). Louisa had a split second decision- duck or be hit.

Obviously, she ducked, the shield slamming into the tree that Louisa had used as cover. Louisa picked it up quickly, raising it in time as Karla bought a short sword down on her head. Louisa tripped Karla up with a Judo sweep and while the Hunter was down, Louisa disarmed her, taking the arrows for her own.

She threw the shield back at Thalia, who managed to dodge it.

She grinned cheekily at the five Ares kids before sprinting off.

Louisa's sword shimmered and became her red and gold watch. She managed to load her bow with a Hunter's arrow and fired up at a medium high branch. It was a net arrow. Two Hunters fell from their hiding spot, encased in the net, which had tied itself to the tree. The net spun one way and then the other, suspended two feet from the ground. They shouted insults after Louisa, who had already moved on.

Five minutes later, when Louisa reached another clearing, she had set eight traps- trip wires, that triggered nets or ropes to lift the one who had tripped the wire stuck until someone cut them down, or hanging upside down by their ankles. Other trip wires dropped godly strength stink bombs on the tripee's head.

* * *

Percy and Annabeth were fighting together, the Hunters silver flag (with the full moon and a silver bow and arrow on) five metres from their current position.

There was no way they could get the flag. The Hunters had rigged various traps and had various arrows, all with special, different abilities, fired in Percy and Annabeth's direction.

If it hadn't been for Louisa, who cleared a three foot bush and shot three arrows (at once) in the same moment, Percy and Annabeth wouldn't have got the flag.

Two of the arrows were 'flash-bang' arrows that blinded them momentarily. The third was another net arrow, which trapped the two Hunters who had been guarding their flag.

"Where'd you come from?"

"The forest." Percy ran to get the flag. Annabeth knew Louisa's random timing had been what they had needed- an element of surprise.

Percy returned.

You take the flag. We'll stop anyone trying to get it back."

"Why've I gotta take it? Why don't Annabeth take it? She did all the plannin'." Annabeth was grateful to be recognised for her work.

"Guys, we don't have time to argue. Louisa, you take it. You're the fastest."

"But-"

"Just take it!" Percy shoved the flag into her hands. "Now, go! We'll cover you."

The boundary line- the creek- was in sight. Running towards it, on the opposite side was Thalia, with the Athena flag. Annabeth scowled. Thalia noticed and shot her a cheeky grin.

Louisa put on a burst of speed.

Then the impossible happened.

She and Thalia jumped the creek at the same time.

It was a tie.

The conch horn sounded, signalling the end of the game. Louisa and Thalia still held the flags, staring at each other in disbelief.

Chiron appeared a minute later, along with a few demigods. It didn't take long for the Hunters and the Campers to file in.

"Do we have a tie?" Chiron asked, almost smiling.

"Yeah." Louisa and Thalia replied truthfully. Louisa flashed a devilish grin.

"Now what?" Percy asked.

"I believe a fight between Thalia and Louisa is required." Chiron said. There was a new light in his friendly brown eyes- one of hope. The Hunters had won consistently, almost a hundred times in a row. Now there was a chance they could break that winning streak. "Hand the flags over and stand five metres apart, one either side of the creek." Chiron instructed.

Thalia and Louisa obeyed. Chiron stood on Louisa's side of the creek. He caught her eye and gave an encouraging smile.

"That's a bit unfair." Annabeth quietly told Percy.

"What is?" Annabeth rolled her eyes. He scowled at her, but was smiling sweetly a second later. "What's unfair, Wise-girl?"

"Louisa's got to fight Thalia. The whole camp is putting a lot of pressure on her to win."

"She doesn't look under pressure." Percy pointed out. Annabeth looked at Louisa, noticing that the undetermined demigod's emerald eyes had a slight glimmer of unease.

"She could be trying to cover it up." Percy didn't answer, silently agreeing with his girlfriend.

"Fight!" Chiron ordered.

Thalia pounced, with her sword in hand, on the unarmed Louisa. Louisa ducked to the left, Thalia's sword grazing her shoulder.

Louisa did the natural thing and punched Thalia in the stomach. Thalia staggered back, winded.

Thalia regained her balance and stood up straight, her blue eyes flashing with power. Louisa stared her out.

Thalia's shield unfolded on her arm. Normally the sight of Aegis unsettled people, but Louisa's expression remained blank. What was she doing?

"Are you gonna fight or not?" Thalia asked impatiently.

"Mmm…" Louisa hummed, her tone monotonous.

Thalia's impatience got the better of her. She ran forward, her sword raised.

Louisa's sword appeared in her hand as Thalia's sword narrowly missed her throat.

The two exchanged jabs and blocks, parries and slashes. Thalia smashed into Louisa with her shield. Louisa fell heavily, losing her blade. She cursed in Latin and rolled away as Thalia stabbed down.

* * *

Louisa took a turning point five minutes into the fight. Her expression suddenly hardened towards Thalia.

Thalia charged Louisa for a third time.

In a matter of seconds, Louisa had grabbed Thalia's wrist, somehow made Thalia drop her sword. Louisa twisted and flipped Thalia over her shoulder.

Thalia pushed herself up, her back throbbing in pain. She glared up at Louisa, who stood her ground a metre and a half away.

The Hunter scrambled to her feet. Louisa's sword had disappeared and Thalia's own blade was too near Louisa to risk retrieval.

If Louisa was going to fight with hand-to-hand combat, then it was only fair for Thalia to do the same.

Thalia didn't charge Louisa this time. Instead she started walking sideways, in a circle. Louisa copied, keeping twenty paces from her opponent.

Louisa had a sudden burst of inspiration and sprinted towards Thalia unexpectedly. Thalia met her head on, bracing herself to struggle against Louisa.

But Louisa had other ideas. She dropped to her knees, allowing Thalia to miss and stumble forward. When Thalia's arm swung back, Louisa grabbed her wrist and stood up, staying in a slight crouch. She flipped Thalia over her shoulder again. Thalia groaned as she landed on her front on the hard ground. Louisa hauled her to her feet and had the Hunter in a headlock a second later. Thalia fought to break free, trying in vain to use her remaining strength. Her left arm was a disadvantage and Louisa knew it.

Thalia hooked her leg behind Louisa's and kicked forward. They both toppled backwards, Thalia gaining a few precious seconds to escape.

Louisa managed to free her bow and three fart arrows. She ran and jumped, firing down at Thalia. The fart arrows exploded in front of Thalia, disorientating her.

Thalia choked on the fart gas. Something collided with her, knocking her to the ground. The air was knocked from her lungs.

Thalia looked up and saw Louisa glaring down at her, holding her knife to Thalia's throat. Louisa was pinning Thalia down underneath her.

Louisa's glare vanished as she grinned with triumph. She got up, holding out her hand. Thalia blinked blankly at her before smiling and taking Louisa's hand. Louisa pulled Thalia to her feet.

"So did Lou win, or did they both win? I'm confused." Percy admitted to Annabeth. She laughed softly, catching Chiron's eye. Percy looked up at their teacher. "Chiron, who won?"

"Louisa did." Thalia announced, surprising everyone. It wasn't like her to admit defeat. "Fair and square." Louisa looked astounded. "You're a good and fair fighter and I respect you for that." Thalia laughed at everyone's shocked expressions.

Louisa gave her a cocky grin, holding out her hand.

"'N' I respect ya for bein' a challenge." They shook hands, grinning at each other.

Suddenly a sea green light momentarily blinded them all. When that faded, they all saw what had caused it.

A hologram floated about Louisa's head.

"Dude, I've got a ninja for a sister!" Percy grinned. Laughter followed before demigods, Hunters and Chiron bowed to Louisa. Percy bounded forward, standing at his new sister's side.

Oddly enough, a sense of relief washed over Annabeth. While Louisa had been undetermined, she had worried a lot as Percy and Louisa had got on great. Annabeth had been _jealous_. Now she could relax and keep Percy for her own.

* * *

**This might be a bit :/ but I did type this, like, **_**forever **_**ago! **


	2. Chapter 2

**To Guest- thank you! **

**And thank you to Amanye- I'll do that thing we talked about here ;)**

* * *

"My mom's place is nearest." Percy told them. Annabeth nodded in agreement while Louisa scowled. She was _fine_. Just a broken ankle.

"I can walk." She growled as they tried to help her up, snatching her arms away and glaring at them. Annabeth shot a glare back. Percy didn't look convinced, but he had quickly learnt not to argue with this unclaimed demigod. She was violent. More-than-Annabeth-violent and he hadn't even thought that was possible.

Louisa pushed herself to her feet, wobbling and grimacing. Still, she refused their help, limping off on her own.

"She doesn't like us, does she?" Percy asked quietly, massaging the back of his neck. Annabeth sighed.

"I don't think she likes anyone."

"I can hear you." Louisa glowered at them over her shoulder. Percy gave a half-hearted wave and a crooked smile, but she looked forward and carried on limping. How she didn't fall over, they weren't sure, but Percy somewhat respected her for just dealing with it.

They reached his mother's apartment ten minutes later. Thankfully, no more monsters appeared out of the crowds and tried to eat them or steal their left shoes- _what was it with left shoes_? Percy asked himself.

Louisa leant against the wall as Percy fumbled in his pockets for his key. She had paled considerably, but she was too stubborn to ask for or accept help.

"Mom?" Percy called as he walked in.

"In here, Percy!" He smelt blue cookies and smiled, his stomach rumbling in agreement. It was nice coming home to blue cookies.

Sally appeared, drying her hands on her 'Best mom' apron. Her smile faltered when she saw their battered, bruised and grubby frames.

"Hi." Percy smiled. Sally mentally shook herself, waving them in.

"Hello, Annabeth. What happened?"

"Couple of _empousi _and _dracaenae_." Sally pursed her lips. "They're dust now, it's OK." Annabeth shrugged indifferently and turned back. "Lou, come on. Sally doesn't bite."

"Can I have a cookie?" Percy asked.

"Five more minutes." Sally laughed. "Who's Lou?"

"Friend of ours."

"Demigod?"

"Yup."

"Claimed or no?"

"No." Sally wrinkled her nose and moved towards the open door. Louisa was still leaning against the wall, heavier than before, doubled up and grumbling Ancient Greek curses.

"What did you do?" Sally asked kindly, trying to take her by the arm and help her inside. Louisa yanked her arm away and sent an icy look at Sally.

Louisa narrowed her eyes at Percy's mother. Why was she just staring at her?

Sally was quiet for a good five minutes; staring at Louisa, mouth agape while awe and mild fear riddled her features.

"_What_?" Louisa demanded angrily, her temper reaching a new height.

"Mom, you OK?" Percy tucked his hand in the crook of his mother's arm, frowning at Louisa as if it were _her _fault that his mother had seemingly lost it.

"I-Is… is… Lou… short for anything?" Sally eventually choked out.

"Louisa." The second her name left her lips, a green glow erupted through the hall. Percy blinked the sudden flash from his eyes, feeling as awestruck as his mother once he had.

He didn't get a chance to say anything further as his mother let out a startled, somewhat relieved sob. He had to catch her as her knees buckled.

"Mom?" He asked worriedly. Her eyes were closed, tears streaming down her pale cheeks.

"Percy…" Annabeth called softly. He looked at her over his shoulder and then back at Louisa.

The trident hologram was fading, but it was still visible.

He had a sister.

So cool!

"Mom, come on." He urged kindly, pulling his mother's arm about his shoulders and lifting her to her feet. "Annabeth, get Mom a tea, will you?" Annabeth nodded and vanished into his home. He glanced back at Louisa- his new sister- and tried to keep his voice as level as possible. "Come on, Lou. I think we need to talk."

"No." She defied outright.

"Your ankle."

"My mom's on her way." Louisa bunched her fists. "I ain't stayin' here." Sally opened her eyes then.

"Your… mom?" She struggled to get the words out. "Did… she adopt you?"

"Yeah. Why?"

"When?"

"What's with all the questions?!"

"_When_?" Sally persisted, trying to stand up straighter. Louisa muttered another foreign curse and glared at Sally defiantly.

"I was in an orphanage 'til I was five. I ran away 'n' was adopted when I was nine."

"You survived four years on your own?" Percy quizzed.

"Yeah. So?"

"But… that's dangerous. Especially for… kids like us." She seemed to like glaring at people more often than usual today.

"I don't care." She put her weight on her uninjured ankle and started to turn away.

"Wait!" Sally called, finding strength from somewhere. She pulled away from her son and hurried forward, grabbing Louisa by the wrist. It was a miracle the daughter of Poseidon didn't lose her balance as she whirled round in anger, drawing her wrist back harshly. "Please…" Sally's voice was soft and trembling. "I… just want to talk."

"Well, I don't." Louisa started to leave again. Percy returned to his mother's side, supporting her by the elbow with a warm, comforting smile. His mother still appeared to be debating with herself about something, her eyes shining evidently with tears.

"You're twins!" She blurted out, her grip tightening on Percy's arm. Louisa stopped on the first step down, hand on the rail for balance. She didn't look back. "Percy," Sally looked at him, reaching up with a shaking hand and caressing his cheek. "I'm so sorry, I should've told you. Poseidon said… he said not to and…"

"Twins." Louisa repeated. The word tasted bitter on her tongue, horrible. "You kept him 'n' got rid of me then?"

"No!" Sally sobbed. Annabeth peered around the doorframe curiously. "I didn't get rid of you! Poseidon took you away while I was sleeping!" Annabeth disappeared and returned moments later with a wad of tissue. Sally murmured her thanks, dabbing at her eyes before continuing. "I… I wanted to keep both of you! I would have struggled to manage, but… you were my children… I couldn't bear the thought of giving you up- either of you." She shook her head, hiding her face in the tissue.

"Nice ta know ya stayed in contact." Louisa shot back, disappearing down the stairwell.

Percy and Annabeth managed to coax and distraught, almost hysterical Sally back into the apartment. Percy sat with her, talking in soft tones and reassurances. He understood that Poseidon had to take one of them and that it was for their own safety, as well as Sally's.

He didn't understand why Louisa had stormed off.

OK, being put up for adoption and 'abandoned' for nine years wasn't ideal, but she could have tried to be a bit more lenient. Her biological mother was there and willing to make amends, yet she had merely walked off.

It took a good half hour to calm Sally down. Her hands still shook as she sipped at her tea, but she was better.

"My gods…" Sally scolded herself under her breath. "I'm so sorry. You shouldn't see me like this."

"Mom, it's OK." Percy smiled. "We're all allowed crazy moments." Sally gave a small, grateful smile and held her arms out to her son.

"I should've told you about her."

"Did Dad say not to?" Percy felt his mother nod against his shoulder. "Better if you hadn't then." Sally sniffled.

"I woke up that first morning home and found her cot empty." She drew away from her son, wiping at her eyes with a fresh tissue. "Poseidon had left a note- too dangerous to keep both of you. Best if you were separated until the time was right."

"Did he say what… dangers they would bring?" Annabeth asked softly.

"He didn't go into detail, but opposites clash, he said. Louisa would grow up too reckless, too confined in a home life. She needed a sense of freedom, of… self-improvement or some rubbish." Thunder rumbled in the sky, but Sally ignored it. "You were the easier option." She smiled weakly at her son. "Not easy, but easier. Less likely to be destructive."

"Two sides of the ocean." Annabeth chipped in. Sally nodded in agreement.

"Poseidon told me Percy would be a calmer, more manageable version of the sea. That's why he excels in controlling water, healing and the likes. She is more likely to be the… other side of the sea. Hurricanes, tsunamis and earthquakes."

"All that jazz." Percy mumbled.

"That storm." Annabeth offered, her eyes narrowly as she thought furiously. "That wasn't you!"

"I told you it wasn't me!"

"But it wasn't Poseidon either, I get that now. It was Lou."

"But she didn't do anything. She was just…" Percy strained his memory.

"Arguing with someone, wasn't she?" Annabeth frowned. "One of the Hermes lot." Percy hunched his shoulders. "Oh, you're helpful."

"I'm going to go and have a lie down." Sally decided.

"Let me know if you need anything." Percy said. Sally thanked him and tottered off to her room, closing the door behind her.

Percy instantly turned to his girlfriend, his eyes shining excitedly. "I have a sister!"

"I know."

"That's so cool! I should find her." He jumped to his feet, but Annabeth was instantly in his way.

"Whoa, Percy. She could be anywhere by now. Her… adoptive mom was coming to get her, remember?"

"Oh…" His smile faltered slightly. "I'll find her." He vowed.

"You're going to IM her, aren't you?"

"Yup." He grinned. Annabeth rolled her eyes at him, but he had the idea now and there was no changing his mind now.

"Alright, but make it quick. She'll come back here just to skin you." For some bizarre, Seaweed-Brain reason, he found that funny.

* * *

**So… how's this?**


	3. Chapter 3

She had only been at Camp for a week and it was obvious that Louisa and Clarisse did not get on- so obvious, even _Clovis_ knew.

"Leave me _alone_." Louisa growled, trying to pull her arm free from Clarisse's iron grip.

"You can't avoid initiation any longer, midget."

"Clarisse, just leave it." Percy intervened. He was getting bad vibes from the unclaimed demigod, but he wasn't sure why or how.

The daughter of Ares ignored him, obviously. Percy was slowly working her out of this initiation thing she had going, but it was difficult, taxing work.

Louisa glared defiantly at Clarisse, drawing up her knee and landing a solid kick to Clarisse's knee, dislodging it with sickening ease. Clarisse fell away and Louisa stalked off, folding her arms and ignoring Clarisse's siblings' protests.

One of her brother's stormed forward, not letting this go easily. Two of the others were braving holding Clarisse still to set her knee back.

"Hey!" He demanded. "Where'd you think you're going, shrimp?"

"Leave me alone." She spat over her shoulder, quickening her pace.

"I don't think so." He grabbed at her arm, but she snatched it away, whirling around in anger.

"_Leave me alone_!" Thunder rippled through the darkening sky. "How are ya so _stupid_?!" She threw her hands up and then that was the most shocking of developments; a hurricane ripping from the ground and storming after the Ares kids.

The hurricane dissipated as she clenched her fists, her lips moving in a silent curse. She was trembling from head to foot, anger coursing through her at unstable extremities. Thunder boomed again, the sky so dark with storm clouds; it could have easily passed as night. If you looked, you could see the waves slamming onto the sand, reaching heights of twenty feet and battling with each other to cause havoc to the beach.

Ares' children made a shield wall, weapons at the ready. Louisa turned her glower on them, not noticing a satyr half-trotting and half-running off.

"Stand down!" One of them yelled.

"_Fuck_ off then!" She threw her hands out again, palms down to the ground. The ground trembled, cracking and crumbling as water exploded from it in fierce jets. Thunder tortured their ears again, so unbelievably loud; it was like there were storms in their ears.

Grover stumbled up the steps to the Poseidon cabin just as the door opened. Percy stood there in his pyjamas- boxer shorts and a Camp Half Blood T-shirt- rubbing sleep from his eyes and looking expectantly at his best friend. His bed-hair was atrocious- Grover had never thought his friend's hair could get any messier.

"I didn't set a storm off, I swear."

"No, I know. Get some jeans on and hurry!" Percy stared at him. Grover bleated and drew his pan pipes. Percy's eyes widened at the sight of them and he darted back into his cabin. Even after amazing improvement in his pan pipe music, Percy still struggled with Grover playing them.

He was ready in ten seconds flat, running a hand through his hair to try and tidy it to some degree. He jogged after Grover, yawning and trying to wake himself up fully.

Another clap of thunder and he was wide awake, staring up at the sky as it started to rain. Sheets of ice water poured down, faster and heavier than Percy had ever seen. Unfortunately for the rest of the campers, he was waterproof.

The next thing he saw was a line of campers lined up in a shield wall with weapons in hand. Some of them were in armour, others in regular clothes and one of them in pyjamas. Percy thought they had good taste.

Then he saw who they were fighting.

A girl, his age thereabouts, was yelling Ancient Greek obscenities at her opponents, the sky and just in general as she clearly struggled against something. She kept furling and unfurling her fists.

"Grover…" Percy started uncertainly.

"Watch it, man. She does some weird stuff."

The campers advanced, someone shouting a 'final warning' to back down. Something snapped and she drew her hand back, sea green energy blazing in her palm. She yanked her hand forward and the energy snapped out, throwing the assembled campers flying back.

Percy noticed then- she was also dry.

As if reading his mind, a green trident erupted into life above her head, as if it wasn't obvious enough.

"Well then…" Percy pressed his lips together, poking Grover into being waterproof as well.

"Do something!" The satyr insisted.

"Oh, right… my bad." Percy grinned sheepishly and Grover rolled his eyes. "Hey!" Percy ran towards the girl, recognising as the new camper that nearly decapitated him in training. Louisa, her name was. "No flooding my camp!" Her sea green eyes were fiery and that weird sea green energy spiralled up her arms. Percy slowed his pace, holding his hands up to show he was unarmed and not going to hurt her. "How do you do that?" He motioned at the power writhing about her arms. She didn't answer, setting her jaw defiantly. "OK, can you stop all this?"

"I'm tryin' to." She stared at her hands, clenching her fists. Percy edged forward, gripping her kindly by the wrist. Her head snapped up and he held her gaze, smiling reassuringly.

"It's OK." He promised. "We'll sort this out; you've just got to calm down." She inhaled deeply and let the breath out slowly. Percy did the slow breathings with her and was relieved when the tension seeped from her gradually.

He was even more relieved to see that the rain had stopped, the storm clouds were rolling out and that the waves had resided into calm, inviting waters. The ground had settled and the wind had eased to a cool breeze.

Percy smiled. "There. That's better." She nodded, running her hands through her hair and dislodging the hairband, snapping it back up into a ponytail as the other campers moved forward, walking cautiously. "It's OK!" Percy called.

"We're cold!" Somebody shouted.

"Since when did Poseidon have another brat?" Someone else shouted. Louisa bristled, but Percy waved her back.

"Perseus Jackson, what in the name of Hades do you think you're doing?!"

"It wasn't me!" Percy pleaded. So much for being one of the most observant people at Camp- Annabeth had missed the whole bloody thing.

He explained, waving his hands around and making sound effects to emphasise his point. "And now I have a sister!" He grabbed Louisa, dragging her into the limelight and keeping her trapped there with a brotherly arm about her shoulders. She did _not_ look happy about that.

"All that and you're not tired?" Annabeth studied Louisa carefully.

"It's… weird." She settled with.

"You're telling me! I don't know what she did, but there was this green-blue light and she was throwing it around and kicking ass big time! I want to do that!" He grinned excitedly, his eyes eager.

"Um… OK… light?" Annabeth glanced back at her boyfriend's new sister. Louisa sighed, cupping her hands as if she were catching water. Between her palms, a sphere of sea green energy no bigger than a tennis ball materialised. "Wow… I haven't seen that before. How do you do it?"

"Dad taught me."

"That's so unfair!" Percy protested instantly. The sea green energy vanished and Louisa was glaring at him. "What?"

"It's _unfair_?" She demanded. "I can't control what I do! I get angry 'n' it gets out of control! I don't do anythin' 'n' it gets worse!"

"If you don't use your powers, it builds up and kind of bursts out?" Annabeth quizzed. Louisa nodded. "And your temper- does that trigger it?" Louisa nodded again, bunching her jaw. "Percy's emotions sometimes trigger his powers, but I haven't seen anything like what he's told me."

"I'm destructive." Annabeth's eyes brightened and she understood something.

"That's it!" Percy stared at her blanky. "You're calm and cool-"

"Thanks."

"Don't interrupt." He smiled sweetly. "But she's tempermental with violent tendencies-"

"Ah, ya noticed."

"Don't interrupt!" Annabeth sighed, running a hand through her hair. "Come on, we've got a lot to talk about. I wonder if Chiron's back yet…" She mused, more to herself than them.

"Daughter of Athena," Percy translated, "She talks to herself sometimes, but I don't know what she's on about half the time." Louisa gave an agreeing smirk and they followed Annabeth, Percy poking people as he passed and having them dry instantly.

Having a sister sounded cool! And it would be even better if she could teach him new tricks.


End file.
